Historically, electric devices have been powered by cable from a mains outlet or the like. However, disposable batteries have been used for a long time in portable devices, such as radio receivers and tape recorders, toys, torches etc, and in today's portable electronic devices the use of customised rechargeable batteries is clearly dominating. It is widely accepted that the development of advanced digital equipment, such as laptop computers, video cameras, personal digital assistants (PDA) and mobile phones, has led to, and also been highly dependent on, major advances in battery technology.
Any battery, rechargeable or not, has a finite duration given the power consumption circumstances. Obviously, the longer duration the better. When an electronic device is turned on but not actively used, the device is often referred to as being in standby mode. In standby mode the power consumption is generally fairly constant and well known, although it may vary e.g. due to temperature variations or the age of the battery. The estimated remaining duration, expressed in standby time, can therefore easily be calculated by withdrawing the lapsed time in standby mode from the expected total standby mode duration. Apart from standby mode, other well known modes having a more or less known associated power consumption may be defined, for which the remaining duration can be calculated in a similar manner. In mobile phones of the so-called 2nd generation, e.g. GSM (Global System for Mobile communications), such a mode is talk mode, which is when a mobile phone is actively used for data transmission to and reception from a base station in the mobile system network. Therefore, the total time for which a 2nd generation mobile phone can be used from a fully charged battery is often expressed in both standby time and talk-time as a technical characteristic for the device. Furthermore, information about the current remaining standby time and talk-time is generally presentable on a display of the device, such that the time to battery recharge can be estimated by the user.
Needless to say, once a part of the battery power has been consumed, the remaining useable time in the respective mode will decrease, and likewise the skilled person will realise that the total duration for which the device can be used is not the sum of the current standby time and talk-time. Furthermore, apart from the two mentioned modes, which can only be used one at a time, other functions of the device that can be simultaneously used will affect the power consumption and the total remaining duration of the battery before a recharge is needed. Such functions may be the use of the device to play games or driving a media player, such as a radio receiver, a DVD drive or an MP3 player. Furthermore, the device may e.g. be set to use an auxiliary transceiver such as a Bluetooth chip or IR transceiver, and may have display back-light capabilities. The use of any of those functions or others will obviously add to the power consumption to a more or less known degree. It would be difficult, if not impossible, to calculate the remaining time in all combinations of used functions, and it would definitely not serve any purpose to present the remaining time for all those different combinations.
Consequently, for electronic devices which can operate in different ways or modes rendering different levels of power consumption, it is often difficult for a user of the device to estimate how long a battery will last. In the case of mobile phones the two different modes identified above are generally the only ones for which the run time of the device to next recharge is given. When the user operates the device for other purposes or uses other functions the power consumption will be affected, and therefore also the remaining run time. In most mobile phones, the remaining charge of the battery can be calculated by the microprocessor of the phone, and consequently the remaining time expressed in any of the predetermined modes can be displayed, even if the phone is operated with further functions than those defined by those predetermined modes. However, the software for performing the calculations generally needs some time to sample and integrate the current power consumption in order to recalculate the estimated remaining time in e.g. standby time or talk-time. Furthermore, the remaining time is most often not given in the default window on the display, but must be fetched from a status window by some kind of command. All these factors contribute to make it difficult for the user to make a good estimate on when the battery will be empty and a recharge or battery change is needed. Furthermore, the run time experienced by the users often does match their expectations which stem from the promised standby time, since other functions have also been used even if talk-mode has not been entered.